As a driving source for power-window device, wiper device, sunroof device, and the like, each of which is provided to a vehicle such as automotive vehicle, an electric motor, which is operated by a power supply such as a battery installed in the vehicle, is used in most cases.
In order to adapt the electric motor to these devices, it is necessary to reduce the revolution number of this motor to a predetermined revolution number. For this reason, as the electric motor for use in such applications, conventionally, a motor with speed reduction mechanism (motor apparatus) in which a speed reduction mechanism is attached to an electric motor main body, and which is constituted as one unit, is used.
In the motor with speed reduction mechanism, a gear case is secured to a motor case (yoke) of a motor main body, and the speed reduction mechanism is housed in a bathtub-shaped housing unit formed in a gear case. As the speed reduction mechanism, a worm gear mechanism, which provides a great reduction ratio by using a small-size device, is used in most cases, the rotation of a motor shaft (rotational shaft) is reduced to a predetermined revolution number by the speed reduction mechanism, and transmitted to an output gear. Furthermore, the opening of the housing unit is occluded with a cover, and the output gear protrudes the outside of the gear case via a through hole of the cover.
In this motor with speed reduction mechanism, a sealing structure for occluding the housing unit is provided to a cover so as to prevent water such as rainwater, dusts, and the like from intruding into the gear case.
For example, Japanese Patent Application Laid-Open Publication No. H11-146594 discloses a motor with speed reduction mechanism in which a ring-shaped seal member, which is held in sliding contact with an outer peripheral surface of an output gear, is attached to an inner peripheral edge of a through hole of the cover, and a seal member (O-ring) is placed between an outer peripheral portion of the cover and an opening end of the gear case.